The primary purpose of this study is to investigate and systematically explicate the doctrine of God found in the writings of John Wesley. This thesis consists of seven chapters: the incomprehensible God, the revelation of God, the Trinity, the attributes of God, creation, the providence of God, and conclusion. Wesley was biblical and practical in explaining God. He also defended a holistic view of God: that the omnipotent and omniscient God is at the same time personal, just, and holy. However, in the historical background of the eighteenth century when the traditional doctrine of God was challenged, Wesley emphasised that God is a personal, holy, triune God. Wesley’s doctrine of God is the doctrine of “the old religion”, which wants to return to the root of the original Christianity of the Bible and “the primitive Church”. Thus, the root of this doctrine is in the Bible and “the primitive Church”. In this sense, this doctrine is orthodox and ecumenical. A characteristic feature of this doctrine is its emphasise on the harmony of God’s attributes and on the balanced activity of the three Persons of the triune God in the process of salvation. Thus, for example, while he stressed the moral attributes of God, he did not limit any natural attribute of God. Further, seeing salvation as a whole work of the triune God, Wesley did not fall into an unbalanced view of salvation that lays emphasis on one Person of the triune God in the process of salvation. Wesley characteristically understood God as personal. For him, the personal God means that he is relational and social interacting with intelligent beings. Thus he rejects God’s pantheistic and panentheistic relation to the world. This personal God enjoys having fellowship with human beings and working together with them. This determines how salvation is worked out and how the kingdom of grace on earth is established. In a word, the personal God desires synergism in salvation and his kingdom of grace. The dynamic of Wesley’s doctrine of God was in his spirituality and his vision for establishing ‘the kingdom of holiness and happiness on earth’. In sharing this spirituality and vision, his doctrine of God can be a new challenge today and can radically transform the world.